Hydraulic and pneumatic actuators are well known in the art. Indeed, a conventional hydraulic or pneumatic actuator normally consists of a hollow cylinder and a piston able to fit sealingly therein and adapted to translate relative to the cylinder in an axial direction between an open position and a closed position. The piston sealingly engages the inner surface of the cylinder so as to create a chamber whose volume varies with the position of the piston. A pressurized fluid can be supplied to, or withdrawn from, the chamber in order to force and change in the chamber's volume and thereby change the position of the piston relative to the cylinder.
A common use for such an actuator is as a hydraulic actuator for heavy machinery, such as a grapple, an excavator or the like. Such heavy machinery run large gasoline or diesel powered engines to power hydraulic pumps, which in turn pressurise hydraulic fluid. This machinery often comprises large mechanical arms, or booms, driven by externally mounted hydraulic actuators. When the actuator is extended, the piston is exposed to an environment where it is vulnerable to damage which could compromise the functioning of the hydraulic actuator. In addition, the piston may simply become dirty as unwanted contaminants, metallic dust particles for example, are deposited on the surface of the piston. Repeated contraction and expansion of the actuator can cause these contaminants to enter into the chamber thereby damaging the piston seal and the inner surface of the cylinder. Both such aspects of exposure have a detrimental effect on the functioning of the actuator and can lead to actuator failure.
The following U.S. and Canadian patents disclose prior art devices for protecting actuator pistons.
U.S. Pat. No. 4,936,193, issued Jun. 26, 1990 to STOLL, describes a protective device comprising a series of cylindrical guard sections operable to protect a piston rod when in an open position. The first of the series of guard sections is fixed to the extremity of the cylinder from which protrudes the piston rod, and the last of the series is fixed to the outer extremity of the piston rod itself. The sections decrease in diameter in a telescopic manner, such that they may be stowed in an overlapping arrangement, one inside another, in a closed position and extended together in an open position. Each guard section comprises an inwardly extending flange at its outer extremity and an outwardly extending flange at its inner extremity. In use, the inwardly extending flange engages the outwardly extending flange of the next guard so as to prevent the complete drawing apart of the individual guard sections in the open position. However, this design is relatively complex comprising a number of sliding elements and engagements.
U.S. Pat. No. 5,386,652 issued to RAMUN, U.S. Pat. No. 6,843,005 issued to CLAPPER, U.S. Pat. No. 5,152,351 issued to RIEGER and Canadian patent No. 1,176,915 issued to MARTIN all disclose actuator protection devices for heavy machinery wherein a piston protector is attached to an outside extremity of a piston rod and is operable to cover at least portion of the exposed piston rod when the cylinder is in an open position.
However, while each of these devices may aid in protecting a piston rod in an exposed open position, there is still a continued need for an improved actuator for heavy machinery that overcomes at least some of the above-mentioned disadvantages.